Vacuum Thermal Etching of Germanium and Silicon Surfaces

The surface structures formed on {111}, {110}, and {112} surfaces of silicon and germanium heated in the temperature ranges 900°–1380°C for silicon and 650°–937 °C (mp) for germanium have been detailed. The changes in topography were found to be markedly dependent on the degree of undersaturation maintained during heating, as well as on the temperature range. The {111} surface of germanium was particularly sensitive to surroundings of the crystal. The proximity and shape of the surroundings influenced the free evaporation rate from the heated surface. Either "worms" or oriented pits formed according to whether the degree of undersaturation was low or high. The various topographical changes are discussed in terms of bond breaking, surface atom mobilities, and free energy minimization.